The present invention relates generally to N-(substituted) maleimides and, more specifically, to certain mono- and polyfunctional N-aryl maleimides, as well as to resins and other products incorporating the same.
A variety of N-substituted maleimides are known in the literature in a variety of uses. For example, bis-maleimides are well-known in composites, and bis- and higher-functional maleimides have been utilized as crosslinkers in a variety of applications.
Monofunctional N-alkyl and N-aryl maleimides have extensively been used to improve the heat stability of homo- and especially copolymers prepared from vinyl monomers. Typically, the bulk resins comprise ABS (poly-(acrylonitrile-co-butadiene-co-styrene)) or a polyblend of poly-(acrylonitrile-co-butadiene) and poly-(styrene-co-acrylonitrile); PVC (poly(vinyl chloride)); SAN (poly(styrene-co-acrylonitrile)); PMMA (poly-(methyl methacrylate)); and the like. The maleimides can be copolymerized with other monomers such as acrylonitrile, butadiene, styrene, methyl methacrylate, vinyl chloride, vinyl acetate and many other comonomers. A more preferred practice in the industry is to produce copolymers of maleimides with other monomers such as styrene and optionally acrylonitrile and to blend these with ABS and SAN resins. In any event, the polymer compositions are adjusted so that the copolymers are fully compatible with the bulk resins (e.g., ABS and/or SAN) as shown by the presence of a single glass transition point (T.sub.g) as determined by differential scanning calorimetry (DSC). Maleimide-containing vinyl resins and their use in the manufacture of parts for automobiles, electrical and electronic machinery and appliances, because of their good heat resistance, impact resistance and moldability, are generally described, for example, in CA872324, JP-A-62036442, JP-A-62288655, JP-A-01079248, JP-A-02004810, JP-A-02147610, U.S Pat. No. 3,652,726, U.S. Pat. No. 3,676,404, U.S. Pat. No. 3,766,142, U.S. Pat. No. 4,039,734, U.S. Pat. No. 4,374,951, U.S. Pat. No. 4,381,373, U.S. Pat. No. 4,605,700, U.S. Pat. No. 4,683,275, U.S. Pat. No. 4,874,829, U.S. Pat. No. 4,879,343, U.S. Pat. No. 4,914,138, U.S. Pat. No. 4,954,571, U.S. Pat. No. 4,983,669, U.S. Pat. No. 5,028,651, U.S. Pat. No. 5,091,470 and U.S. Pat. No. 5,136,052. All of the above are incorporated by reference herein for all purposes as if fully set forth.
Among the numerous maleimides described in the literature for use in this application, N-phenylmaleimide (NPMI) appears to be the monomer of choice as it displays excellent properties as a material to improve heat resistance. The major drawbacks are its high toxicity and deep yellow color which can impart dark color to the finished molded articles, especially at high monomeric usage. Thus, compounds possessing the desirable properties of NPMI but without such drawbacks would be distinctly advantageous.
While it appears that a wide variety of N-((substituted)phenyl)maleimides have been described in the literature as possible alternatives to NPMI, one that has not specifically been mentioned is N-(2,3-dimethylphenyl) maleimide. It has now been discovered that N-(2,3-dimethylphenyl) maleimide, a pale yellow to white solid, appears to be less toxic than NPMI. Further, it has been surprisingly discovered that homo- and copolymers of N-(2,3-dimethylphenyl) maleimide are readily compatible with ABS, SAN and a variety of other resins.
It should be noted that N-(2,3-dimethylphenyl) maleimide is, in and of itself, known and has been described for uses including, for example, in compositions for inhibiting adhesion of shellfish and algae (GB1533067 and U.S. Pat. No. 4,111,879) and as an antimicrobial agent (JP-A-02240002; Igarashi et al, Nippon Kagaku Kaishi (9), 1616-19 (1989)). Homopolymers and copolymers of N-(2,3-dimethylphenyl) maleimide, however, have apparently not been specifically described, particularly for use in improving the heat resistance of bulk resins. In addition, bis- and higher-function variations of N-(2,3-dimethylphenyl) maleimides have apparently also not been specifically described.